U.S. Sen. Rand Paul's neighbour pleaded guilty Friday to a federal charge for tackling the lawmaker in an attack his attorney says was triggered by a dispute over lawn maintenance.

Rene Boucher entered the guilty plea in federal court in Bowling Green, Kentucky, to a charge of assaulting a member of Congress. Paul suffered broken ribs in the attack last year.

"He is looking forward to closure on all of this once and for all," said Boucher's attorney, Matt Baker. "He still feels as though he has the weight of the world on his shoulders."

A judge set a June 15 sentencing date for the retired anesthesiologist in his late 50s. Federal prosecutors have signalled they will seek a 21-month prison sentence. Baker said he will ask for probation. The charge carries up to 10 years in prison and a $250,000 fine.

Boucher also agreed to pay restitution to Paul, according to media reports. The amount will be determined at sentencing.

Paul, a former presidential candidate, was attacked Nov. 3 while mowing his lawn at his home. A close friend of Paul's said the Republican senator had gotten off his riding lawn mower to remove a limb when he was tackled from behind. Paul has said he never saw the attacker because he was facing downhill and wearing ear protection from the noise of his lawn mower.

Paul suffered multiple broken ribs in the attack. He returned to Washington less than two weeks later but developed pneumonia when he returned to Kentucky.

Paul has said he's recovering well from the attack.

Some residents of the gated neighbourhood in Bowling Green had speculated the attack was motivated by a dispute over yard debris.

Baker said Friday that the attack was a "complete lapse in judgment" by Boucher.

"He and his neighbour have had a long-standing disagreement, and it just finally boiled over over this yard issue," the attorney said in a phone interview.

In comments to police, Boucher indicated the attack was not politically motivated, according to court documents. Instead, it had to do with a property dispute, it said.

Boucher is free on bond and living in his house next to the senator's home, Baker said. The conditions include that Boucher have no contact with Paul or the senator's family.

That includes Boucher's daily walks with his dog. He agreed to either follow a route that takes him away from Paul's home, or to take his dog to a nearby park, Baker said.

In arguing for no prison time, Baker said, he'll note that Boucher's record had consisted of a speeding ticket before the attack.